November 1, 1898.] 



KNOWLEDGE. 



245 



Caligus torpedinis. 

 From Hi-Uer. 



majority of which are Copi'poda in disguise, some attain 

 to relatively large dimensions. Many of them are per- 

 fectly symmetrical, difl'ering from the free-living types 

 most obviously by the flattened body with its diverse flaps 

 and skirt-like expansions, and by the suctorial mouth 

 which gives to the whole group its title Siphonostoma. 

 Others carry bizarre monstrosity to such an excess that all 

 typical shape and structure arc blurred or lost in a kind of 

 travesty and caricature. 



I'or study, the species Caliiim curtits 

 (Miiller), common on the cod, and 

 Lrpfiiphtlifiim siihiwnis, Kroyer, from 

 the salmon, may be commended because 

 they are easily attainable. Viewed from 

 above they show two principal sections 

 separated by a more or less wasp-like 

 waist. The upper section is the cephalo- 

 thorax with three of the trunk segments 

 in coalescence. Behind this is the free 

 fourth trunk-ring, followed by the lower 

 section, which consists of the large 

 genital segment, the terminal segment, 

 and the usual setiferous caudal fork. 

 On the back of the cephalo-thorax are 

 two minute eyes, and at its top the 

 first antenna;. Underneath will be 

 found the second antenn:c, hook-like. 

 There are supplementary hooks on 

 either side of the mouth, which is 

 made up of the two lips and the 

 mandibles, and goes by the name of rostrum or siphon. 

 Outside it are a pair of " palps." Then follow two 

 pairs of maxillte and a horny " furcula." The three 

 trunk-segments have three pairs of swimming legs to 

 correspond, the broad flap-like expansions at the base of 

 the third pair being especially conspicuous. The fourth 

 segment has a slender pair of legs. To the genital seg- 

 ment in the female are attached the long pair of egg- 

 strings. Between the two genera above-mentioned there 

 is a distinction easily perceived. In the Calii/us only will 

 be found a pair of sucker-disks, which from their brightness 

 and their position on the front margin were not un- 

 naturally at one time supposed to be the creature's eyes. 

 Such forms as the above can fix 

 themselves with tenacity ; can move 

 over their hosts with freedom ; 

 and can swim with vigour in the open 

 water. Under these circumstances, a 

 fish, having no hands, is deplorably 

 incompetent to decline or to dislodge 

 his unbidden and unwelcome guests. 

 Specimens of several genera batten on 

 the unwieldy sunfish. The parasite of 

 the sturgeon, Dichclestium aturionis, 

 Hermann, is much segmented, and 

 has no leaf-like expansions. With it, 

 in the first respect, may be contrasted 

 the Stiiilia.v inonstrosus of Nordmann, 

 which, in the female, has no segmen- 

 tation at all. ' hoiiilracantlius horridus, 

 Heller, which resides in the Mediter- 

 ranean on Goiiiujoijzo, ia symmetrical, 

 if nothing else. On the other hand, 

 f Hocus (/ohinus (Fabricius) is so far 

 from pretending to symmetry that, but 

 for the long twisted egg-sacks, it might 

 Tid«s. From HeUer. ^6 supposed to be only a piece of pro- 

 toplasm dancing the Can-can. 

 As in all other parts of the subject, so here, only a 



Chondracanthus hor- 



selection has been possible of a very few out of many 

 competing topics of interest. Of the parasitic Copepoda a 

 great number are known, but 

 probably a vast number remain 

 to be discovered, the chances 

 being that almost every new 

 fish, if properly examined, 

 would yield a new parasite. 

 It will not, perhaps, be easy to 

 discover a more singular form 

 than the Spln/rion lavifjatum 

 of Quoy and Gaimard, which 

 has been taken from time to 

 time in the Southern Hemi- 

 sphere. In the earlier half of 

 this century so little was 

 known of its real character 

 that, so lately as 1813, it was 

 mixed up in a heterogeneous 

 group of " zoophytes " with 

 echinoderms and worms and 

 polyps and infusoria. It is now known to be one of those 

 "oar-footed" crustaceans which have neither oars nor feet, 

 and which live with their muzzles buried in their favourite 

 fishes. This epicurean existence seems to favour eccentricity 

 of structure, and for those who desire the grotesque and 

 the unfamiliar there may still be as good parasites in the 

 sea as ever came out of it. 



Dioeus gobiiius (Fabricius). 

 From Steenstrup and Liilken. 



SELF-IRRIGATION IN PLANTS.-III. 



By the Rev. Alex. S. Wilson, m.a., b.sc 



RAIN in its passage through the air dissolves small 

 quantities of ammonia, nitric acid, and other 

 substances, and this is no doubt an additional 

 gain to plants which collect and accumulate rain- 

 water in proximity to their roots and other parts 

 where absorption occurs. The water that gathers in leaf- 

 cups especially is likely to contain materials useful to 

 plants, since it is often quite brown with the remains of 

 insects that have fallen in and been drowned. 



To creeping ants and beetles water presents an impas- 

 sable barrier. For this reason, when a gardener wishes to 

 protect a plant from their attacks he puts it on the top of 

 an inverted flower-pot and places this in the middle of a 

 flat dish containing water, where it stands, as it were, on 

 an island inaccessible to the auta, many of which perish in 

 their ineflectual attempts to reach it. Similarly, the water 

 in the leaf-cups of the teasle surrounds and isolates the 

 stem ; the leaves and flowers are protected as by a moat 

 from the attacks of creeping insects. 



Although such protection is perhaps their original use, 

 leaf-cups in many instances appear to have assumed an 

 additional function, ilr. F. Darwin has observed that 

 certain hairs in the leaf-cups of the teasle emit proto- 

 plasmic threads into the water ; this also occurs in the 

 case of Silphium. As filaments exactly similar are emitted 

 from certain cells in the little traps of the toothwort, now 

 regarded as a carnivorous plant, there can be little doubt 

 that leaf-cups serve to some extent like the pitchers of 

 Nepenthes and Sarracenia for capturing insects, and that 

 they consequently furnish the plant with an important 

 source of nitrogen. This view is confirmed by the frequent 

 presence of putrefactive bacteria in the water of leaf-cups. 

 It has been found that when a drop of water containing 

 carbonate of ammonia in solution is placed on a leaf, after 

 a time both water and salt disappear. Leaves as well as 

 roots therefore take up ammonia, and this explains why 



